Auxiliary propulsion unit



'March 27, 1934. J. A. M GREW AUXILIARY PROPULSION UNIT Filed Jan. 14. 1931 4 Sheets-Sheet 1 AUXILIARY PROPULSION UNIT Filed Jan. 14. 1931 4 Sheets-Sheet 2 March 27, 1934. J. A,M GREW AUXILIARY PROPULSION UNIT Filed Jan. 14. 1931 4 Sheets-Sheet 3 March 27, 1934. J. A. McGREW 1,952,272

AUXILIARY PRQPUL S I ON UNIT Filed Jan. 14. 1931 v 4 Sheets-Sheet 4 is W | \x w k 0 Patented Mar. 27, 1934 PATENT OFFICE AUXILIARY PROPULSION UNIT John A. McGrew, Albany, N. Y.

Application January 14,

20 Claims.

This invention relates to power transmitting mechanism and particularly to such mechanism in auxiliary power or propulsionunits for locomotives.

comotives for supplementing the power of the locomotive at certain times, as, for example, when starting and accelerating the locomotive and its train of cars, and they are usually appliedto one of the trucks of the locomotive tender. Each of such units comprises a steam engine adapted through suitable pipe connections to be energized by steam from the locomotive boiler, a power shaft rotated by the engine, a train of gearing between the power shaft and an axle of the truck, and means for controlling the steam supply to the engine and for controlling thegear train so that it will be automatically thrown into action when the engine is started.

The present invention contemplatesthe provision of improved mechanism for entraining the driving shaft of an auxiliary propulsion unit of this type with an axle of the truck on which it is mounted; of improved means for controlling the supply of steam to the engine thereof; of means for absorbing the inevitable shocks incident to the meshing of the gears of the-unit; and of other important improvements, as will appear hereinafter.

Referring to the accompanying drawings in which one embodiment of my invention is illustrated by way of example:

Figure 1 is a longitudinal section of the unit takenon a central vertical plane, in which is somewhat diagrammatically illustrated the piping arrangements; Y Figure 2'is a longitudinal section through the frame of the unit taken on a vertical plane which includes the axis of one of the engine slide valves;

Figure 3 is a transverse section through the frame taken on line 3-3 of Figure 2;

Figure 4 is a transverse section on line 4-4 of Figure 2;

Figure 5 is a longitudinal section on a larger scale, of the throttle valve mechanism;

Figure 6 is a sectional view of a pneumatic blow off valve associated with the propulsion unit;

Figure 7 is a greatly enlarged fragmentary view in side elevation and partly diagrammatic, illustrating the progressive meshing of the gearing; and

' Figure 8 isa fragmentary sectional view of the gearing showing the construction and arrangement of the shrouds associated therewith.

Suchdevices are used in connection with 10- 1931, Serial No. 508,753

The auxiliary propulsion unit illustrated in the drawings as enclosed within frame 10 is adapted to be mounted on the forward truck of the 10- comotive tender, but this particular location of the unit is to be understood as merely illustrative and in no way restrictive of the scope of the invention.

Referring to Figure l, in which the valves and piping arrangement for supplying air and steam to the auxiliary locomotive unit are somewhat diagrammatically shown, the numeral 1 designates a pipe or conduit leading from the main air reservoirrof the locomotive to the valve 2 which is a two line air controlling valve of standard type positioned in the locomotive cab for actuation by the engineman. The valve operating handle in this figure is shown in its right hand or closed position 18a and is adapted to be moved to a corresponding positon 18b upon the left hand side of the center line of the valve 2, which is the starting position, and to the vertical positon 18c which is the running position.

Conduit 3 connects one side of the valve 2 with the pneumatic blow off valve 94 of the auxiliary locomotive unit and a pipe line i, provided with two by-passes 5 and 6, connects the other side of the valve 2 with the starting mechanism of the unit. An ordinary check valve '7 is provided in the by-pass 5 to check the flow of air in the direction from the valve 2 toward the unit.

The numeral 8 designates a pipe through which steam is supplied from the superheater header of the locomotive (not shown) to the cylinders of the auxiliary propulsion unit. A throttle valve 9 of any suitable type is disposed in this pipe line and is adapted to control the flow of steam therethrough.

As a means for operating the throttle valve 9 by means of the pressure of air supplied through the valve 2, the following mechanism is provid ed. An air cylinder 11 is connected'in the bypass piping 6 so that air may be admitted to the head of the cylinder and move the piston 12 longitudinally therein. The piston rod 12', is operatively connected with the valve rod 9' of the throt: tle valve 9 by means of the pivoted bell crank lever 13. The cylinder 11, throttle valve 9, and lever 13 may all be conveniently supported by a suitable bracket 14 secured to a stationary part of the locomotive.

That portion of the by-pass 6 which together with pipe 4 connects the cylinder 11 with the auxiliary propulsion unit is adapted to communicate with the cylinder through the side wall thereof and the orifice of the pipe 4 is adapted to be covered by the piston 12 when the various elements are disposed in their inoperative positions.

The frame 10 of the power unit is a casting with which the engine cylinders, the steam and exhaust passages, the throttle valve housing, etc. are integrally formed. This casting, or frame, is mounted on the truck by means of a three-point suspension. At its rear end the frame is formed with transversely spaced aligned bearings 15 which surround the driven axle 16 at opposite sides of a gear wheel 17 secured centrally on said axle, and at its front end the frame is yieldingly suspended from the truck bolster 19 by means of a bolt 20 depending from the bolster and passing loosely through an aperture in a lug 210 3 the frame, the bolt being surrounded by coil springs 22 and 23 which are respectively interposed between the lug and the bolster and between the lug and a seat 24 supported on the lower end of the bolt. In the event of failure of this spring connection, a hook-like extension 25 of the frame disposed over the front axle 16 of the truclc will engage the latter to support the unit temporarily.

A power shaft 2'7 mounted in bearings 28 cf the frame 10 is adapted to be driven by two double acting engines respectively located at opposite sides of the longitudinal center line of the frame. The engine cylinders, cast integral with the frame, are shown in cross-section in Figures 3 and 4, and designated respectively by the numerals 29 and 30. Since the present invention is not concerned with the details of the engine, the drawings merely indicate the cylinders and valve housings and the steam and exhaust passages associated therewith, for the purpose of illustrating the path of the steam.

Figure 3 shows in cross-section cylindrical slide valve housings 31 and 32 associated respectively with the engine cylinders 29 and 30. The valve housing 31 associated with cylinder 29 is also shown, in longitudinal section, in Figure 2, and it will be observed that this housing is formed with central ports 33 which open into a steam space 34, and with ports 35 and 36 which open respectively into steam passages 37 and 38, which lead to' the two ends of the engine cylinder 29. Valve housing 32 is formed with similar ports communicating with steam space 34 and with the two ends of cylinder 30. It will be understood that, in the operation of the engines, piston valves (not shown) reciprocate in housings 31 and 32'. Passages 39 into which the ends of housing 31 open are exhaust passages and communicate with the atmosphere through opening 40. The piston valve in housing 31, for example, functions in one position to connect steam space 34* with steam passage 38 and to connect steam passage 37 with exhaust passage 39, thereby admitting steam to one end of the cylinder and exhausting steam from the other end; and in the opposite position, the valve connects steam space 34 with steam passage 37 and steam passage 38 with exhaust passage 39, reversing the steam and exhaust connections to the cylinder. It will be seen from Figures 3 and 4 that the openings 40 of the exhaust passages are located at the lowest point in the path of the steam, so that condensate will drain out through these openings by gravity, thereby eliminating the necessity for drain cocks or the like.

Referring now to Figures 1 and 5 for a description of the regulating valve mechanism 'associated with the propulsion unit and the gear entrainment mechanism, the numeral 41 designates a piston valve adapted to control the admission of steam from a steam chest 42 to the steam space 34 into which the central ports 33 of the valve housings 31 and 32 open. Steam chest 42 is supplied with steam through the pipe connections 8 leading from the superheater header of the locomotive. Flexible joints may be provided in the piping 8 to permit the piping to adjust itself to the relative movement between the locomotive and tender. Valve 41 is slidable in a central cylindrical housing 43 cast integral with frame 10 (see Figure 3). This housing is formed with an admission port 45 communicating with steam chest 42, and in the position shown in Figure 5, the valve 41 closes communication between steam chest 42 and steam space 34. The steam space 34 may be provided with any suitabletype of automatic drain cock such as at 44 in Figure 1. When the valve 41 is moved to the right (Figure 5), by mechanism presently to be described, steam chest 42 will be placed in communication with steam space 34 and the engines will be set in operation.

The operating means for the regulating valve 41 comprises a pneumatically actuated piston 46 working in a cylinder 4'7 secured to one side of a partition wall 48 in axial alignment with the valve. Compressed air is adapted to be admitted to the right hand end of cylinder 47 as seen in Figure 1, by the tube 4 connected to the throttle valve actuating mechanism and the manually operable valve 2 located in the locomotive cab in convenient reach of the engineman. As illustrated in Figure 5, which shows the regulating valve mechanism on a larger scale, the valve 41 carries a stem 51 which passes, with substantial clearance, through an axial aperture 52 in the valve and is slidably supported near its inner end in a seat 53 carried by the valve in al gnment with aperture 52. Stem 51 is adapted to have a limited axial movement with respect to the valve, and for this purpose it carries on its inner end a nut 54 which in the closed position of the valve is slightly spaced from seat 53. The outer end of stem 51 is enlarged and formed with a conical valve 56 which seats on a conical surface around aperture 52 when the valve 41- is in closed position. The outer end of stem 51 is connected to a rod 57 which passes through a stufiing box in the cyl nder head 58 of the valve. Rod 57 is adjustably connected to one end of a link 59, the other end of which is connected to a rod 60 which passes through a stufiing box 61 of cylinder 4'? andaxially through the piston 46, to which it is secured, and thence passes through an aperture inpartition 48 and has its end threaded into a follower 62 which is formed with a head 63 adapted to engage the circular fianges of a tumbler gear of the transmission, as will be pointed out in detail hereinafter.

In order to get rid of the condensate which accumulates in chest 42, there is applied at the lowest point of said chest a pneumatically operated valve 94. The present invention is not concerned with the construction of this valve per se, but it is illustrated sufficiently in Figure 6 to enable a clear understanding of its operation. The casing of this valve is bolted or otherwise secured to frame 10 over a port 95 which opens at the bottom of steam chest 42, and the casing is formed with a passage 66 communicating with port 95 and with a cavity 67 housing a ball valve 68. Ball 68 will normally be forced by steam pressure against a seat 69 formed around a central opening in a partition 70. On the other side of thispartition there is a chamber 71 which communicates with the atmosphere through an opening 72. To the right of chamber 71 there is a cylinder 73 separated from chamber '71 by a partition 74 formed with a centralopening through which projects a stem 75 secured to a piston 76 located in cylinder 73. Piston 76 is adapted to be moved to the left against the action of a spring76 by air pressure admitted to the right hand end of cylinder 73 through a tube connection 3 leading to the enginemans valve 2. In starting the engines of the auxiliary pro pulsion unit, the engineman will first move the handle of the valve 2 to the starting position18b, thus admitting fluid pressure to both conduits 3 and 4. Through pipe 3 the pressure fluid will pass to the blow off valve 94, moving the piston 76 to the left and causing the stem 75 to forcibly unseat the ball 68 and vent the chest 42 to the atmosphere. It will be observedthat this valve will open automatically whenever the pressure in the steam chest 42 is reduced sufficiently to permit ball 68 to fall from its seat by gravity, thus draining the chest 42 automatically whenever the steam pressure is reduced or absent. Through pipe 4 the pressure fluid will pass to the cylinder 11 of the throttle actuating mechanism whereupon the piston .12 will move to the right (Figure 1) and open the throttle valve 9 by means of the connections 9', 12, and 13, thus admitting steam through the conduit 8 to the steam cavity 42 of the engine.

The valve handle is next moved from starting position 185 to .running position 180 whereupon the pressure fluid supply is cut off from the pipe line 3 permitting drain cook 94 to close without afiectng the throttle valve 9, the latter not being closed until the valve handle is returned to the initial or. closed position 18a.

When pressure fluid is admitted to the throttle valve, the movement of the piston 12 for a short distance exposes the port in cylinder 11 to which the outlet piping of the by-pass 6 is connected and permits air to pass through the piping 4 and by-pass 6 to the propulsion unit at approximately main reservoir pressure. In passing to the actuating cylinder 47 this air encounters the reducing valve 77 which permits it to enter the cylinder 47 at the minimum pressure necessary for the operation of the valve 41 and the tumbler gear pusher 62. The numeral 78 denotes a safety or pressure relief valve, the function of which will be later described. 7

Upon admission of air to the right hand end of cylinder 47 (Figure 1) the piston 46 will move to the left against the pressure exerted by the spring 64. In the initial part of this movement, pilot valve 56 will be unseated permitting steam to flow from the steam chest 42 through a tube 65 to the right hand side of piston valve 41 (Figure 5) and thence through the pilot valve to the left hand side of the valve 41, thereby equalizing the pressure on the two sides of the valve piston. The continued movement of piston 46 will then move the piston valve 41 to the right (Figure 5) to open communication between the steam chest 42 and the steam passage 34, which, of course, will result in setting the engines in operation.

Gear wheel 17 on truck axle 16 is adapted to be entrained with the power shaft 27 through the instrumentality of a gear wheel 79 keyed on said shaft and a floating, or tumbler, idler gear 80, which constantly meshes with gear 79 and is adapted to move automatically into mesh with gear 17 in the initial operation of the engines. As indicated in Figure 8, the gears 80, 17, and 79 are provided at each side with circular flanges or shrouds 81, 82, and 85, respectively, which may be formed integrally with the gears or which preferably comprise separately formed members rigidly secured upon the shafts or axles 86, 16, and 27 of the gears. The shroud members 81, 82, and 85 are of external diameters which are equal in each case to the diameters of the pitch circles of their respective gears. With this construction it will be seen that when the tumbler gear .80 is in. full meshing engagement its shrouds 81 are in rolling contact with the shrouds 82 and 85 of the gears 1'? and'79 and thus bottoming of the teeth is prevented and the provision of a very sturdy and smoothly running gear train is attained.

The shrouds 81 of the tumbler gear 80. are adapted to roll and slide upon the inclined guides 83 which are integrally formed with or otherwise secured to the bottom wall of the frame or housing l0,.as shown in Figures 1, 7, and 8. Normally the teeth of the gear rest against a stop 84, secured to the bottom wall of casting 10 in front of the inclined guide 83, with the head 63 of the follower spaced rearwardly a slight distance from the gear as illustrated at 630. in Figure 7. When compressed air is admitted to cylinder 47 the piston 46 therein moves to the left carrying with it the follower 62 and the valve stem 51 and pilot valve 56, unseating the valve 56 to cause equalization of pressures on the two sides of the regulating valve piston 41, as heretofore pointed out, and taking up the lost motion between the stem 51 and valve 41. On continued movement of piston 46 to the right (Figure 5), the valve 41 will also move to the right. The follower head 63 during this movement is brought into contact with the gear 80 at position 80a and moves it to position 8012 when the valve 41 is line and line with its seat. When further movement has caused the valve 41 to open by a small amount (about 3% the head 63 of the follower 62 will have been moved to point 630 whereupon it willh'ave moved gear 80 to position 88c. At this point steam is admitted to the engines in sufficient quantity'to cause them to operate and rotate shaft 27 and gear 79 in a clockwise direction, as indicated by the arrow in Figure 1. Since gear 79 is constantly in mesh'with tumbler gear 80, the latter will rotate in a counter-clockwise direction which will move the tumbler gear up the incline 83, due to the rolling of the shrouds 81 on the inclined guide surface, and cause effective meshing engagement of the tumbler gear with gear 17, whereupon these gears will be brought into full mesh by the interaction between. their respective teethfthef shrouds 81 being liftedslightly out of engage-Q ment withthe inclined guide surface 83. The follower 62, after the admission of sufficient steam to start the engines, continues its movement toward the left along with the valve 41, but during this continued movement serves no further function than providing a safety device for ensuring the eifective meshing of the gears in the event of the occurrence of slippage or recoil, as hereinafter described. When the regulating valve 41 is fully open and tumbler 80 is in full mesh with gear 17, as at 8001 the head 63 of the follower will remain at 6302 and will be spaced from-the teeth of the tumbler so as not to interfere with the rotation thereof.

When it is desired to discontinue the operation of the auxiliary propulsion unit the engineman will move his valve handle to closed position 1841,

wherein it vents the piping 4 to the atmosphere, relieving .the pressure on the left hand side of piston 12 allowing the piston 12 to return throttle valve 9 to closed position. Check valve '7 in by-pass 5 will open and permit the passage of air from pipe 4 to the atmosphere. Spring 64 will then move piston 46 to the right which will result in the return of follower 62 and regulating. valve 41 to their normal positions, shown in Figure 1. Steam will be shut off from the engines and power shaft 27 and gear wheel '79 will come to rest, but of course gear wheel 17 will continue to rotate with axle 16. Tumbler therefore will be driven by gear wheel 17 until forced from meshing engagement therewith by reason of its counter-clockwise bodily movement about the relatively stationary gear '79, and the tumbler will continue its bodily, or planetary, movement about gear 79 as it slides down the incline 83 under the action of gravity, until brought to rest against stop 84.

It frequently happens that, in meshing, the teeth of gears 80 and 17 do not meet properly and considerable recoil is experienced by the idler or tumbler gear '80 due to the collision between it and the gear 17. The force of this recoil is transmitted directly from the gear 80 to the follower 62 and thence to piston 46 whereupon the shocks are cushioned or absorbed by the compressed air in the cylinder 47. In order that the pressure in cylinder 47 may not be built up to a point at which its shock absorbing value would be nullified, the pressure relief valve '78 is inserted in the air inlet conduit 4. This valve 78' is set to maintain the pressure in the cylinder at that point which is found desirable for the best results in providing a buffer for the meshing mechanism as just described. In the absence of this recoil absorbing device, especially when the gear 1'7 is rotating very rapidly, these shocks would be transmitted directly to the operating mechanism, which would result in considerable damage thereto.

The reduction of the initial pressures for starting the auxiliary propulsion unit by means of the reducing valve 77 and the provision of the safety valve '18 for preventing the building up of excess pressures in the cylinder 4'7 are highly important features of my invention since there is a wide variationin the air reservoir pressure of different locomotives, these pressures generally being between 90 and 130 pounds. Typical settings for the valves 7'? and 78 for auxiliary engines of the type described would be, for example, about 60 pounds for the reducing valve '7'? and about 70 pounds for the safety valve 78. I From the foregoing it will be understood that the meshing of the tumbler gear 80 with the gear 17 is eifected by the rolling movement of the tumbler gear up the inclined guide 83' under the influence of the driving gear '79 and that the complete meshing of the gears is accomplished by the tooth pressures due to the interengagement of the teeth of the gears 80 and 1'7. There is also provided by means of the follower 62, and the piston 46 operating in the air cylinder 47, an effective buffing arrangement for receiving and dissipating any shocks which may be sustained by the tumbler gear 80 incidental to the meshing thereof.

While the particular embodiment of the invention illustrated in the drawings has been described with much detail, it will beobvious to those skilled in the art that many changes can be made in the form, construction and arrangement of the elements without departing from the principles of the invention or from the scope of the invention as defined in the appended claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In an auxiliary power unit comprising a steam engine, a valve controlling the supply of steam to said engine, a driving gear, a driven gear, a tumbler gear constantly in mesh with said driving gear and movable by rolling contact with a guide surface into mesh with said driven gear, and a follower moving synchronous- 1y with said valve and capable of being engaged by said tumbler gear, said follower constituting an auxiliary means for ensuring the preliminary meshing engagement of the teeth of said tumbler gear and those of said driven gear.

2. In an auxiliary power unit comprising a steam engine, in. combination, a control valve for said engine, a driving gear, a driven gear, a tumbler gear constantly in mesh with said driving gear and movable by rolling. contact with a guide surface into mesh with said driven gear, a follower capable of being engaged by said tumbler gear, said follower constituting an auxiliary means for ensuring the preliminary meshing. engagement of the teeth of said tumbler gear and those of said driven gear, and a common. motor connected to said control valve and said follower for operating them, said motor being actuable independently of the steam supply for said engine.

3. In combination with a locomotive, an auxiliary power unit comprising a frame mounted on a load supporting axle and adapted to house a steam. engine, a driving shaft journalled in said frame adapted to be driven by said engine, means for operatively connecting said driving shaft with said axle, a steam chest in said frame connected to the boiler of the locomotive, a control valve mounted in said frame and controlling the con nection of said steam chest with said engine, and a motor mounted in said frame and controllable independently of the steam supply for operating said control valve.

4. In combination with a locomotive, an auxiliary power unit comprising a frame mounted on the truck of the locomotive tender and adapted to house a steam engine, a driving shaft journalled in said frame adapted to be driven by said engine, means for operatively connecting said driving shaft with an axle of said truck, a steam chest in said frame connected to' the boiler of the locomotive, a control valve mounted in said frame normally closing communication between said steam chest and said engine, a pneumatic motor operably connected to said control valve, and means controllable from the cab of the locomotLve for admitting and exhausting compressed air to and from said motor.

5. In combination with a locomotive, an auxiliary power unit mounted on a truck of the 10- comotive tender and adapted to house a steam engine, a driving shaft journalled in the frame adapted to be driven by said engine, means for operatively connecting said driving shaft with an axle of said truck, a steam chest in said frame connected to the boiler of the locomotive, a valve controlling the connection between said chest and said engine, and a pneumatically operated blow off valve connected to said steam chest adjacent the bottom thereof.

6. In an auxiliary power unit comprising a steam engine, a driving gear adapted to be operated by said engine, a driven gear, a tumbler gear constantly in mesh with saiddriving gear, aninclined guide on which said tumbler gear is adapted to roll into mesh with said driven gear, a slide valve controlling the supply of steam to said engine, a pneumatically operated piston between said slide valve and said tumbler gear, connections extending from one side of said piston'to said slide valve, and a follower adaptedto contact said tumbler'gear and connected to the other side of said piston. l

'7. An auxiliary "power unit for locomotives adapted to be applied to a truck, comprising a frame pivoted at one end on an axle of the truck, means for suspending said frame from the truck bolster, said frame having a hook-like extension from its other end disposed over another axle of the truck and adapted to come into engagement therewith in case of failure of said means.

8. In combination with a truck, an auxiliary propulsion unit frame having bearings at one end pivoted on an axle of the truck, resilient means for suspending said fame adjacent its other end from the truck bolster, and a hook-like extension from said other end disposed over another axle of the truck and adapted to come into ongagement therewith upon failure of said resilient suspension to provide a temporary support for said frame.

9. In combination with a truck, a propulsion unit frame having bearings pivoted on an axle of the truck, a bolt depending from the truck bolster, said frame having a lug adjacent its other end formed with an aperture through which said bolt extends, and two coil springs surrounding said bolt and interposed respectively between said bolster and lug and between said lug and a seat carried by the lower end of said bolt.

10. In combination with a frame for auxiliary locomotive propulsion units comprising a casting forming a pair of engine cylinders located symmetrically at opposite sides of the central vertical longitudinal plane of the casting with steam and exhaust passages to and from said cylinders, and forming a cylindrical housing between said cylinders and a steam chest extending above said housing, a valve reciprocable in said cylindrical housing adapted to control communication between said steam chest and said steam passages, and a motor mounted in said frame and operably connected to said valve.

11. In a power unit for locomotives or the like, a driving gear, a driven gear, a tumbler idler gear adapted to be moved into a position where it is in mesh with both of said first named gears,

a reciprocating member for initially moving said tumbler gear, fiuid pressure actuated means for resiliently operating said reciprocating member so as to absorb shocks which might be sustained incidental to the meshing of the gears.

12. In a power unit for locomotives or the like, a driving gear, a driven gear, a tumbler idler gear adapted to be moved into a position in which it is in mesh with both of said gears, a reciprocating member for moving said tumbler gear through a portion of its travel to said position, pneumatically actuated means for operating said reciprocating member, a conduit for placing said means in communication with a source of compressed air, and means in said conduit for reducsure actuated ,meansis provided with a pressure relieving means forpreventing the accumulation of too high a pressure in said first named means to effectively cushion and absorb said shocks.

14:. The combination as set forth in claim 6 in which. pressure controlling devices are associated with said pneumatically operated piston whereby shocks transmitted to said follower incidental to the meshing of said gears may be cushioned and absorbed.

15. In an auxiliary locomotive propulsion unit, in combination, a regulating valve therefor, a fluid pressure actuated motor for said regulating valve, a throttle valve for supplying steam to said unit, a fluid pressure actuated motor for actuating said throttle valve, an operators valve for supplying fluid pressure to said throttle valve motor and means associated with said motor for supplying fluid pressure to said regulating valve motor upon actuation of said throttle valve motor beyond a predetermined point.

16. In an auxiliary locomotive propulsion unit, in combination, a throttle valve for supplying steam thereto, a fluid pressure motor for actuating said throttle valve, a driving gear associated with said unit, a driven gear associated with an axle of the locomotive, an idled gear adapted to be moved to a position where it is in mesh with both of said first named gears, a reciprocating member for moving said idler gear through a portion of its travel to full meshing position, fluid actuated means for operating said reciprocating member and absorbing shocks incidental to the meshing of saidgears, and means associated with said throttle valve motor for supplying fluid pressure to said fluid actuated means upon movement of said motor beyond a predetermined point.

17. In an auxiliary locomotive propulsion unit, in combination, a throttle valve for supplying steam thereto, a fluid pressure motor for actuating said throttle valve, a regulating valve associated with said unit for further controlling the steam supply, a driving gear associated with said unit, a' driven gear associated with an axle of the locomotive, an idlergear adapted to be moved to a position in which it is in mesh with both of said first named gears, means for initiating the movement of said idler gear, full meshing engagement being attained by tooth pressures, fluid pressure actuated means for operating said first named means and absorbing shocks incident to the meshing of said gears, connections between said fluid pressure actuated means and said regulating valve for operating the latter, and means associated with said throttle valve motor for supplying fluid pressure to said fluid pressure actuated means upon movement of said motor beyond a predetermined point.

18. In combination with a frame for auxiliary locomotive propulsion units comprising a casting forming a pair of engine cylinders located symmetrically at opposite sides of the central vertical longitudinal plane of the casting with steam and exhaust passages to and from said cylinders, and forming a cylindrical housing between said cylinders and a steam chest extending above said housing, and a valve reciprocable in said cylindrical housing adapted to control communication between said steam chest and said steam passages.

19. An auxiliary propulsion unit comprising, in combination, a frame, a motor mounted on the frame, gearing for operatively connecting the motor to a load-bearing axle, said gearing including driving and driven gears and a tumbler gear unit adapted to move into and out of engagement with said driven gear, the driving and driven gears being mounted in the frame to rotate about fixed parallel axes, means for supporting and guiding said tumbler gear unit during movement of said tumbler gear unit toward and from said driven gear, and a separate power operated member adapted to contact with said tumbler gear unit to affect certain of its movements.

20. A vehicle propulsion unit or the like comprising, in combination, a motor, an axle or like member to be driven, a driving gear operated by 

